For spraying contents of an aerosol product in a form of fine foggy particles or discharging contents in a foamed condition, it was conventionally the case that compressed gas such as carbonic acid gas (CO.sub.2) was filled into an aerosol container as a propellant to be dissolved within the contents.
For making the compressed gas dissolve within the contents, a specified amount of contents is first loaded into the container and compressed gas is then loaded into the container at a high pressure. Since the compressed gas is dissolved into the concentrate (contents), it is necessary to apply a high pressure exceeding an internal pressure of the final aerosol product in an equilibrium state.
Explanations will now be given based on a case of a general aerosol product containing therein compressed gas having an Ostwald absorption coefficient (hereinafter referred to as simply "Ostwald coefficient") of 1 as well as contents and wherein the volumetric ratio of the contents is approximately 60% and the volumetric ratio of the compressed gas approximately 40% of the total capacity of the container in case an internal pressure within the container is 0.6 MPa (hereinafter all given as gauge pressure).
As referred herein, the Ostwald coefficient simply represents numeric values of a gaseous volume (ml) dissolved in 1 ml of solvent at temperature t.degree. C. in case a partial pressure of the gas is set to 760 mmHg. In case the temperature is identical, the dissolution ratio is proportional to pressure.
Hence, it is necessary to first inject contents into the container corresponding to approximately 60% by volume under atmospheric pressure, followed by injection of compressed gas of 1.5 MPa. A pressure P of gas to be injected and corresponding to 40% by volume based on an equilibrium pressure within the container of 0.6 MPa (40% by volume of compressed gas and 60% by volume of aerosol) is given by the equation EQU P.times.0.4=0.6.times.0.4+(0.6.times.0.6).times.1,
so that the above value of 1.5 MPa can be obtained. As a general formula, the following equation (1) can be obtained. EQU P.sub.1 =P.sub.2.times.{.chi.+.beta.(1-.chi.)/.chi. (1)
While it is presupposed in this equation that the compressed gas does not dissolve into the contents until the loading of the compressed gas is completed, the compressed gas actually starts to slightly dissolve within the contents during the loading process so that a maximum pressure in the above case is slightly less than 1.5 MPa and approximately 1.4 MPa.
However, conventional aerosol containers can generally not bear even such a degree of pressure. Even if a container should bear this pressure, drawbacks are caused such that a fixing (crimp) of an aerosol valve become loosened. In case of using a container capable of bearing such a high pressure, manufacturing costs will remarkably increase.
Therefore, it is conventionally performed that a separate large sized pressure resistant container is used for the manufacture of aerosol liquid which is sequentially loaded into individual aerosol containers. This method still presents drawbacks in that facilities costs will be largely increased and is also accompanied by increased number of steps during manufacturing.
In a conventional aerosol product using a single-walled can for compressed gas products, the interior pressure of the container gradually decreases each time spraying of the contents is performed. Accompanying this, the amount of dissolved compressed gas is also decreased whereby it becomes difficult to maintain an action of making the foggy particles of the contents fine. Due to this reason, it is required to set the initial pressure as well as the loading rate for the gas high.
In the case a false operation (e.g. the product is used in an inverted posture while the specification prescribes that it should be used in an erected posture), only gas is sprayed so that the pressure of the product is remarkably decreased. It is known for conventional methods for solving this problem wherein a weight is provided at a tip of a tube provided at a valve, while this method is not very reliable due to reasons that the weight might not work in a sufficient manner.
It has then been proposed for an aerosol product with the aim of solving this problem as disclosed in Japanese Unexamined Patent Publication No. 253408/1996 utilizing a double-chamber container including an inner cylinder and an outer cylinder with which it is aimed to restrict decreases in the amount of dissolved compressed gas accompanying the increase in number of spraying.
In this aerosol product utilizing a double-chamber container, the contents are loaded into the interior of the inner cylinder while compressed gas is dissolved into the contents, and a spatial portion between the inner cylinder and the outer cylinder is loaded with compressed gas as a pressurizing agent such as liquefied petroleum gas (LPG) or nitrogen. Since the inner cylinder is a flexible sack-like body made of synthetic resin or the like, the inner cylinder is shrunk by the pressure applied by the pressurizing agent even if the contents included in the inner cylinder is used to be decreased, so that it can be prevented that the amount of compressed gas dissolved in the contents is decreased.
There are mainly two methods for loading compressed gas into the double-chamber container. In a former method that is a so-called TN loading method, the contents (concentrate) are loaded into the inner cylinder, and a valve is crimped to the outer cylinder. Then, compressed gas to be dissolved into the contents is loaded into the inner cylinder from a stem of the valve. Thereafter, compressed gas for depressing the inner cylinder is loaded through a bottom plug of the outer cylinder.
In a latter method, a spray valve is first crimped to the outer cylinder in case of employing a double-chamber container provided with a check valve at a bottom portion of the inner cylinder permitting only flow of gas from the inner cylinder into the outer cylinder (while the flow of contents is not permitted). Then, compressed gas is loaded into the outer cylinder from a stem of the spray valve and the inner cylinder through the check valve. Thereafter, the compressed gas in the interior of the inner cylinder is purged to the exterior from the stem of the spray valve. Accompanying this process, the inner cylinder is in a deflated condition while on the other hand, the interior of the spatial portion of the outer cylinder maintains a condition in which compressed gas is loaded since the check valve is closed. Finally, the loading process is completed by sequentially loading contents (concentrate) and compressed gas to be dissolved into the contents from the spray valve into the interior of the inner cylinder.
However, in a conventional aerosol product employing a double-chamber container, it is required to load compressed gas for making the inner cylinder shrink in addition to compressed gas to be dissolved in the contents, whereby the manufacturing becomes troublesome.
Moreover, since compressed gas needs to be loaded into the spatial portion between the inner cylinder and the outer cylinder in addition to compressed gas to be dissolved in the contents to obtain a desired pressure for the product, it is presented a drawback that the loading amount of contents loaded into the inner cylinder with respect to the inner volume of the outer cylinder is only approximately 60% which is the same level as in the case of a single-walled can.
In the former TN loading method in which compressed gas is loaded into the inner sack through the stem, the space of the interior of the inner sack is smaller compared to the space of the outer cylinder so that the loading pressure at the time of loading a specified amount of compressed gas into the inner sack becomes high. This might result in a drawback that the inner sack would burst.
On the other hand, while TN loading might also be performed in the latter loading method, loading of the inner sack might be performed wherein the compressed gas to be dissolved into the contents (concentrate) is preliminarily dissolved and/or mixed into the contents. This, however, would require the provision of an exterior tank for dissolving and mixing purposes.
Further, in a conventional aerosol product employing a double-chamber container, it is often the case that the contents are in a non-foamed condition (that is, compressed gas (propellant) is not sufficiently dissolved into the contents (concentrate)) so that such products are unsuitable for contents containing a large amount of resin such as resin for hairdressing purposes which is apt to be choked at the stem.
The present invention has been made for the purpose of solving the above problems, and it is an object of the present invention to provide an aerosol product and a method for manufacturing the same wherein the pressure of the product can be made low and the product can be easily manufactured. It is another object of the present invention to provide an aerosol product wherein the loading amount of the contents can be increased compared to conventional products.